Minimally-invasive surgery has evolved to a point where procedures that were unimaginable a few years ago are now routinely performed on a daily basis. Indwelling ureteral stents have been widely used for years. Such stents are placed in the ureter, which is the duct between the kidney and the bladder, for the purpose of establishing and/or maintaining an open, patent flow of urine from the kidney to the bladder.
Ureteral stents may be used to retain patency of the ureteral lumen and to continue normal urinary drainage following the treatment and removal of stones and calculi from kidneys and ureters. To treat this condition, several individual steps are involved. In one procedure, these steps include placing a relatively narrow wire guide through a urethra and a bladder, and then through the ureter and into the kidney. After the wire guide is placed, a catheter is run along the wire guide, dilating the body passage (the urethra and the ureter) as it moves down the wire guide. The access sheath also dilates the body passages as it moves from outside the body, through the urethra, and into the ureter, down the desired location, and into or very near the kidney.
The physician may then remove calculi and stones through the access sheath, using a grasper, a retrieval basket or other device. The access sheath protects the ureter from repeated passage of the retrieval device while the stones or calculi are removed. After the stones are removed, the ureteral stent may be placed into the ureter through the access sheath, using the catheter or a pushing tube to position the stent.
The typical ureteral stent can be composed of various radiopaque polymers, including polyethylene, silicone, polyurethane, and thermoplastic elastomers. These stents are retained in the ureter by a retentive anchoring portion, such as a curved shape, pigtail, coil, J-shape, or hook configuration, at either end of the stent that engages the walls of the bladder and the kidney, respectively. The stent is resilient to allow it to be straightened for insertion into a body passageway and returned to its predetermined retentive anchoring shape when in situ.
There can be problems, however, with ureteral stents, due to pain and discomfort felt by patients. An attempt to reduce problems associated with pain and discomfort to the patient may be addressed through the introduction of pharmacologically active agents in conjunction with the ureteral stent. However, studies have demonstrated that intravesical drug delivery can be limited by the low permeability of the urothelial layer. As such, the urothelial layer of the ureter may serve as a significant barrier to the introduction of pharmacological active agent into the tissue of the ureter. In addition, more of the pharmacological active agent may elute into the urine of the patient instead of the tissues of the ureter, which limits the effectiveness of the pharmacological active agent within the patient.